Transporters expressed during grape berry (Vitis vinifera L.) development are associated with an increase in berry size and berry potassium accumulation

Potassium accumulation is essential for grapevine (Vitis vinifera L.) growth and development, but excessive levels in berries at harvest may reduce wine quality particularly for red wines. In addition to decreasing the free acid levels, potassium also combines with tartaric acid to form largely insoluble potassium bitartrate. This precipitates during winemaking and storage, resulting in an increase in wine pH that is associated with negative impacts on wine colour, flavour, and microbiological stability. For these reasons, a better understanding of potassium transport and accumulation within the vine and berries is important for producing fruit with improved winemaking characteristics. Here two genes encoding KUP/KT/HAK-type potassium transporters that are expressed in grape berries are described. Their function as potassium transporters was demonstrated by complementation of an Escherichia coli mutant. The two transporters are expressed most highly in the berry skin during the first phase of berry development (pre-veraison), with similar patterns in two grapevine varieties. The timing and location of expression of these transporters are consistent with an involvement in potassium accumulation in grape berries.